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RTE1418 Introduction to Radiologic Technique > Image Contrast > Flashcards

Image Contrast Flashcards

1
Q

define image contrast

A

the degree of difference between the light and dark areas of a radiograph

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2
Q

What makes the blacks, whites, and grays on a radiograph?

A

differential absorption

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3
Q

subject contrast

A

component of image contrast determined by size, shape, and x-ray attenuating characteristics of the subject

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4
Q

define differential absorption

A

the difference between photons absorbed and those that penetrate the body

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5
Q

different body structures absorb x-ray photons to ____________ extents

A

different

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6
Q

bones are denser and ________ more x-ray photons than those filled with air such as lungs

A

absorb

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7
Q

attenuation

A

removal of any photons from the primary beam before striking the IR

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8
Q

attenuation is the reduction of:

A

the intensity of an x-ray beam

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9
Q

causes of attenuation:

A

differential absorption
scatter

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10
Q

absorption

A

x-ray photons that are attenuated by the body and do not reach the IR

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11
Q

transmission

A

x-ray photons that pass through the body and reach the IR

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12
Q

What terms describe the beam entering the patient?

A

primary
useful
entrance

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13
Q

primary beam

A

x-ray beam as it is upon exiting collimator and exposing patient

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14
Q

What terms describe the beam leaving the patient?

A

remnant
exit

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15
Q

remnant beam

A

x-ray beam that remains after interaction with patient when exiting the patient to the IR

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16
Q

the remnant beam is composed of what?

A

transmitted and scattered photons

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17
Q

radiopaque

A

body structures that absorb x-ray photons

(bones)

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18
Q

radiolucent

A

less dense body structures that have a lower probability of absorption

(air filled lungs)

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19
Q

photons absorbed show up as _______ on a radiograph

A

white

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20
Q

photons that pass through body and reach IR show up as _______ on a radiograph

A

black

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21
Q

technical term for absorption within the patient

A

Photoelectric Effect

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22
Q

denser tissue _________ the probability of photons being absorbed

A

increases

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23
Q

structures filled with air __________ the probability of absorption

A

decreases

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24
Q

what causes the shades of gray?

A

photons that aren’t completely absorbed or transmitted

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25
Q

high contrast:

A

large differences in brightness

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26
Q

high contrast images have mostly:

A

areas of black and white

only few shades of gray

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27
Q

a high contrast image is also referred as:

A

short-gray scale

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28
Q

short gray scale contrast

A

mostly black and white, few shades of gray

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29
Q

low contrast:

A

small differences in brightness

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30
Q

low contrast images have mostly:

A

areas of gray

only few areas of black and white

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31
Q

a low contrast image is also referred as:

A

long gray-scale

32
Q

long gray scale contrast

A

many shades of gray

very little black and white

33
Q

the total brightness levels that an imaging monitor is capable of displaying is referred to as:

A

bit depth

34
Q

high contrast = ______ gray-scale

A

short

35
Q

low contrast = ______ gray-scale

A

long

36
Q

8 factors that affect image contrast

A

kVp
differential absorption
computer processing and display
filtration
Compton scatter
grids
OID
beam restriction

37
Q

high kVp =

A

low contrast
long gray-scale

38
Q

why does increasing kVp decrease contrast?

A

it creates a more penetrating beam = less differential absorption = longer gray-scale = low contrast image.

39
Q

low kVp =

A

high contrast
short gray-scale

40
Q

Why does decreasing kVp increase contrast?

A

it creates a less penetrating beam, increasing differential absorption, which creates a shorter gray-scale, thus high contrast

41
Q

higher levels of differential absorption =

A

higher levels of contrast

42
Q

Look Up Table (LUT)

A

takes place after the exposure is made and image is processed by imaging system software

43
Q

added filtration will result in:

A

decrease in differential absorption
longer gray-scale thus lower contrast

44
Q

filtration and image contrast has what kind of relationship?

A

indirect

45
Q

higher filtration =

A

harder average beam
lower contrast/long gray-scale

46
Q

lower filtration =

A

softer average beam
higher contrast/short gray-scale

47
Q

Compton scatter

A

x-ray photon that interacts with the body and “scatters” off its original trajectory

48
Q

Compton scatter contributes no useful:

A

information to the image

49
Q

Compton scatter causes a uniform exposure on the IR, causing:

A

a loss of visible image contrast

50
Q

radiographic grid

A

device used to reduce the intensity of scatter radiation in the remnant beam

51
Q

grid clean up

A

ability of a grid to absorb scatter radiation

52
Q

a grid _______________ the scattered photon before it can strike the IR and reduce image contrast

A

catches or attenuates

53
Q

OID and image contrast share a _________ relationship

A

direct

54
Q

increased OID =

A

increase image contrast

55
Q

the most common type of beam restriction is:

A

use of collimation

56
Q

increasing collimation:

A

reduces scatter, leading to a higher image contrast

57
Q

Raw numbers (bar graph) of what is occurring in the body (absorption/transmission) will determine?

A

dose

58
Q

Percentages of what is occurring in the body (absorption/transmission) will determine?

A

contrast

59
Q

effects of kVp on the x-ray beam:

A

increasing kVp creates a more penetrating beam

decreasing kVp creates a more less one

60
Q

effects of kVp on patient dose and on absorption

A

increasing kVp causes a greater dose due to greater % of beam passing through patient, which has a decrease on absorption

vice versa

61
Q

why does increasing kVp increase dose?

A

increasing kVp creates a bigger beam

62
Q

Why does increasing kVp create a bigger beam?

A

more electrons are called over which creates more photons

63
Q

increasing kVp does what to dose and absorption?

A

increases dose, but decreases the percentage of absorption

64
Q

will an increase in kVP cause an increase or decrease to the photoelectric?

A

decrease

65
Q

describe the relationship between filtration and image contrast

A

indirect (greater the filtration the more low photons are removed)

66
Q

a photon that does not strike the IR, what type of photon is this?

A

attenuating photon

67
Q

in the digital age, what is the controlling factor for image contrast?

A

look up table (LUT)

68
Q

a decrease in kVp will cause the average amount of transmission to increase or decrease?

A

decrease

69
Q

why does beam restriction improve image contrast?

A

reduces amount of scatter (less matter = less scatter

70
Q

what are the two different ways an x-ray photon can become attenuated?

A

scatter and absorption

71
Q

what produces subject contrast?

A

differential absorption

72
Q

using one word, describe why increasing OID improves image contrast

A

divergence

73
Q

the total number of grays a system is capable of displaying in a radiograph image is referred to as what?

A

bit depth

74
Q

decreasing kVp will have what effect on differential absorption?

A

increases

75
Q

what is the controlling factor for subject contrast?

A

kVp

76
Q

illustrate how an increase in kVp can cause an increase in dose and a reduction of contrast at the same time:

A

2 kvp lines with one slightly higher and fatter toward when it gets to the bottom

dose is in middle section and contrast is in wider section near bottom

RTE1418 Introduction to Radiologic Technique (12 decks)

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